1. Field of the Invention
The present invention relates to a servo control apparatus, in particular, to a servo control apparatus having a function for optimizing the control gain online using an evaluation function.
2. Description of the Related Art
A variety of devices and methods for measuring the frequency characteristics of a servo control system for a servo control apparatus have been proposed and are widely used to measure transfer characteristics in feed axes of machine tools. In general, response vibration is measured when an object to be analyzed is forcibly vibrated by a vibration generator (frequency sweeping), and time-series data representing the measured vibration is logged in a mass memory. After that, various signal processing techniques are used to obtain a frequency transfer function. In simple measurement, response vibration generated using an actuator as a vibration source is measured and logged to process signals. A vibration circuit is used for an electrical circuit or an optical system.
As a system which optimizes the control gain, a method for fitting a time-series signal to define a basic mode function for a reference model and selecting the result of introducing adjusting parameters into the function as a reference model has been proposed (see, e.g., Japanese Laid-open Patent Publication No. 2015-076024). In this conventional technique, the weighted sum of a plurality of indices (overshoot and rise time) which can be obtained as time-series data and quantified is used as an evaluation function to adjust the PID parameters. Although the meaning of the evaluation function is not concerned, this function typically allows optimization of a compensator for plant control.
In addition, a method for calculating an evaluation value for control characteristics using the error between actually measured time-series data and time-series data of reference responses has been proposed (see, e.g., Japanese Laid-open Patent Publication No. H9-131087). In this conventional technique, an approximate model is stored in an adjusting device and adjusted, and the adjustment result is applied to an actual controlled object.
However, these conventional techniques are based on reference model fitting with the purpose of curve fitting to responses in the time domain. No method has previously been proposed to quantitatively evaluate the difference from a reference transfer function directly in the frequency domain, using frequency characteristics which are available online.